Hard disk apparatuses and optical disk apparatuses are equipped with a motor for rotating a disk. A motor is described in, for example, JP-A 2001-248634. The motor described in JP-A 2001-248634 includes a pair of radial dynamic bearing portions each constituted of a radial dynamic groove and a lubricant with which a radial minute gap is filled. A gas interposed portion is formed at a middle portion between the radial dynamic bearing portions. A ventilating hole is provided inside a shaft of the motor along an axial line so as to extend from a lower end to a position of the gas interposed portion. An upper end of the ventilating hole communicates with the gas interposed portion through a communicating hole. A part of the communicating hole communicates with the outside of the motor. In addition, a lower end opening of the communicating hole is closed with a plug such as a rubber ball.
According to the structure described in JP-A 2001-248634, a disturbance is caused in assembling or driving the motor, so that stress is applied to the shaft or the rubber ball. As a result, there is a possibility that the rubber ball is not fully fixed to the shaft. If a gap forms between the rubber ball and the shaft, there is a possibility that dirt or dust enters the shaft or the dynamic bearing portion.